Will Subwoofer EQ ruin the phase alignment with the mains?

Will Subwoofer EQ ruin the phase alignment with the mains?

Often, folks are concerned about using parametric EQ filters to fix low-frequency repsonse issues in the subwoofers, for fear that the phase shift from the PEQ filters will throw off the alignment with the mains.

In most cases, this isn’t something to be concerned about. 

Here is a matched pair of 4th order Linkwitz-Riley filters.

You can see that adding even a massive 10 dB, hi-Q cut in the LF band has virtually no effect on the phase response through the crossover region. 

Unless the filter you’re adding is sitting right on top of the crossover region, you’ve got no cause for concern. For additional piece of mind, note that the phase derivation caused by the filter is only about 30° (less than a tenth of a cycle), which falls far short of the 120° needed to turn a perfectly aligned summation into a cancellation. Sleep easy!

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